"The development, production and technological applications of carbon nanotube are rapidly growing, due to the unique characteristics of these fibers. Consequently, an increase is also expected in human exposure to such materials. However, little is still known about the safety of the multiple sorts of carbon nanotubes.
Recent studies have suggested that some types of multiwalled carbon nanotubes (MWCNTs) have similar effects as asbestos. This report shows that rigid, long and needle-like MWCNTs induce inflammation and DNA damage in the lungs and in cultured cells, while flexible, long and tangled MWCNTs do not. It appears that the rigidity of MWCNTs is a key feature in triggering a specific inflammatory reaction and in causing cellular alterations involved in cancer formation.
These results provide new information on the adverse effects of MWCNTs and are useful in assessing which forms of MWCNTs require regulatory attention and special safety measures in occupational settings."

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